1. Field of the Invention
The present invention relates to a mounting structure for mounting an electronic component on a circuit board, and more particularly, the present invention relates to a mounting structure for mounting an electronic component on a circuit board with a high positional accuracy.
2. Description of the Related Art
As shown in FIG. 12, an example of a mounting structure of a related art for an electronic component is that surface-mounting lands 11, 12, 13, and 14, on which outer electrodes 21, 22, 23, and 24 of an electronic component 20 are soldered, are provided on a mounting surface of a circuit board 10, such as a ceramic multilayer board, or a printed circuit board. The lands 11, 12, 13, and 14 are provided at positions corresponding to positions of the outer electrodes 21, 22, 23, and 24 of the electronic component 20. To reliably mount the electronic component 20, each of the lands 11, 12, 13, and 14 have a size greater than that of each of the outer electrodes 21, 22, 23, and 24 of the electronic component 20.
The electronic component 20 is mounted on the circuit board 10 as follows. The electronic component 20 is arranged such that the outer electrodes 21, 22, 23, and 24 are aligned with solder pastes printed on the lands 11, 12, 13, and 14, the circuit board 10 with the electronic component 20 mounted thereon passes through a reflow oven (not shown) to melt the solder pastes, and thus, the outer electrodes 21, 22, 23, and 24 are soldered on the lands 11, 12, 13, and 14.
The mounting structure of the related art has the following problems. The melted solder easily adheres to the lands 11, 12, 13, and 14 and the outer electrodes 21, 22, 23, and 24, thus exhibiting good wettability, whereas the melted solders exhibit poor wettability with respect to a board material for the circuit board 10, and a constituent body 20a of the electronic component 20. Due to this, the solder melted as the circuit board 10 with the electronic component 20 mounted thereon passes through the reflow oven does not flow outside the lands 11, 12, 13, and 14, or outside the outer electrodes 21, 22, 23, and 24.
As shown in FIG. 13A, when the land 11 of the lands 11, 12, 13, and 14, and the outer electrode 21 soldered on the land 11 are considered, the melted solder provided therebetween easily wets the land 11 and the outer electrode 21 and adheres to the electrodes and lands due to the wettability of the melted solder.
At this time, the solder simultaneously spreads on the outer electrode 21 and the land 11 in a wet manner, and thus, a self-alignment action is applied to the electronic component so that a maximum superposed area of the outer electrode 21 and the land 11 is achieved. However, when the mounting structure is designed such that the superposed area of the outer electrode 21 and the land 11 does not vary even when the position of the outer electrode 21 is shifted to the upper, lower, left or right side as shown in FIG. 13B, the electronic component 20 may be influenced by a vibration or impact applied from the outside, or by variation in the position at the mounting, causing the electronic component 20 to move freely within a range in which the superposed area remains unvaried. Accordingly, if the solder solidifies after the electronic component 20 is moved, the mounting position of the electronic component 20 may vary.
In order to solve the above-described problems with the mounting structure of the related art, as shown in FIG. 14, Japanese Unexamined Patent Application Publication No. 2000-299548 (Patent Document 1) discloses a land structure for mounting a surface-mounted component 3 on a printed circuit board 1, the surface-mounted component 3 including terminals 3b, 3b each having a narrow width A and protruding from the opposite lateral surfaces of a body 3a. 
Provided on a surface (mounting surface) of the printed circuit board 1 are protruding lands 2, 2 having protruding portions 2a, 2a on which the terminals 3b, 3b of the surface-mounted component 3 are soldered. The protruding portions 2a, 2a of the lands 2, 2 each have a narrow width B corresponding to the width A of the terminals 3b, 3b of the surface-mounted component 3, and protrude inwardly so as to face each other. Solder paste is printed on the protruding portions 2a, 2a of the lands 2, 2, the terminals 3b, 3b are provided on the solder paste, the solder paste is melted through the reflow oven, and the terminals 3b, 3b are soldered on the protruding portions 2a, 2a. 
With the land structure described in Patent Document 1, since the width B of the protruding portions 2a, 2a of the lands 2, 2 is narrow and corresponds to the width A of the terminals 3b, 3b of the surface-mounted component 3, the protruding portions 2a, 2a each have a width substantially equivalent to that of the terminals 3b, 3b. Thus, the surface-mounted component 3 can be mounted on the printed circuit board 1 with a high positional accuracy due to the action of the self-alignment caused by the surface tension of the solder paste melted in the reflow oven.
However, since the protruding portions 2a, 2a have the narrow width B substantially equivalent to the width A of the terminals 3b, 3b, it is difficult to reliably apply the solder paste to the protruding portions 2a, 2a by printing, thereby causing problems of insufficient printing of the solder paste, a decrease in mounting strength of the surface-mounted component 3, and a poor mounting reliability of the surface-mounted component 3 to the printed circuit board 1.